1. Technical Field
The present invention relates generally to a lighting control apparatus for a vehicle which is equipped with a malfunction diagnosis feature and a warning feature to warn about a malfunction of a light source.
2. Background Art
Automotive illuminant devices such as headlamps, fog lamps, or tail lamps are known which have LEDs (Light Emitting Diodes) used as light sources. The illuminant devices are each equipped with a lighting control circuit which turns on or off the LEDs. Such a type of light sources are typically made up of arrays of LEDs or multi-chip LED modules.
The LEDs or the multi-chip LED modules may become defective due to an electric short, a leakage of current causing the LED to have an undesirable impedance, or a change in ambient temperature.
Japanese Patent First Publication No. 2007-112237 discloses an automotive diagnosis system which diagnoses the above malfunction of the LEDs. Specifically, the diagnosis system monitors a change in forward voltage at each of the LEDs and determines whether the LED is malfunctioning or not based on the monitored change. When one of the LEDs is found to be malfunctioning, the diagnosis system lights an LED installed near a driver's seat of the vehicle to warn the driver or other occupants (which will also be referred to as vehicle users below) of the malfunction of the LED.
The above type of a diagnosis system, however, has the drawback in that it is difficult for the users to see the warning lighting of the LED to identify which device is now malfunctioning. The users, thus, need to check the user's manual or call a maintenance service center to know the meaning of the warning message.
The use of the multi-chip LED module as the light source also faces the following disadvantage. When one of the LED chips of the multi-chip LED module is short-circuited, so that it fails to be turned on, it will result in a lack of a luminous intensity distribution of the multi-chip LED module, but the users may not realize such a failure because the multi-chip LED module continues to emit light as a whole. For example, in the case where headlamps attached to the right and left of the front of an automotive vehicle are each equipped with a multi-chip LED module, when one of the LED chips is malfunctioning, the other LED chips work to emit light. It is, thus, difficult for the users to visually identify which of the right and left headlamps is defective. The users may perceive in error that the LED installed near the driver's seat is malfunctioning.